DESCRIPTION (adapted from Abstract): This is a revised application by an experienced investigator seeking 4 years of support for the purification, cloning and characterization of the PC-cell derived growth factor receptor (PCDGF-R). The PI recently identified PCDGF as a novel autocrine growth factor overexpressed in human breast cancer cell (HBCC) lines and in the epithelial cells of ER-/PR- invasive ductal carcinoma with poor prognosis. The PI has shown that PCDGF expression is stimulated by estrogen and mediates estrogen's mitogenic effect, and that PCDGF overexpression is involved in the progression of breast cancer from estrogen dependence to independence, a hallmark of malignancy. Moreover, inhibition of PCDGF expression in ER- HBCC led to inhibition of tumor formation in vivo. PCDGF is a candidate for novel anti-breast cancer therapy based on inhibition of its expression or action. The interaction of a growth factor with its receptor is the initial step in mediating its action. This application proposes to characterize the novel PCDGF-R. For this purpose, the PI recently isolated a HBCC line that overexpresses by 10-fold the number of PCDGF-R seen in MCF-7 and MDA-MB-468 cells. A combination of biochemical, molecular and immunological approaches are proposed. The first one will be to purify PCDGF-R, obtain amino acid sequence information which will be used to synthesize complementary oligonucleotides to screen a human breast cancer cDNA library. The second approach will use expression cloning of PCDGF-R cDNA into PCDGF-R negative CHO cells. Anti PCDGF-R monoclonal antibodies that block PCDGF action will then be developed. The rationale is to use these antibodies to inhibit human breast cancer growth in vivo. The PI states that these studies are innovative since they will provide information on the receptor of a newly characterized growth factor involved in the progression of breast cancer to estrogen independent state. They will also provide a molecular target toward the development of breast cancer therapy that will block growth factor-receptor interaction.